Process for recovery of acyclic diene dimers



United States Patent O PROCESS FOR RECOVERY OF ACYCLIC DIENE DIMERS Glen P. Hamner, Baton Ronge, La., assigner to Esso Research and Engineering Company, a corporation of Delaware Application March 19, 1952,Serial No. 277,422

Claims. (Cl. 260-666) By this invention dimers of isoprene, piperylene, and acyclic hexadienes are formedand separated from cracked petroleum hydrocarbon fractions.

The acyclic C5-Ce dienes can be selectively dimerized by thermal soaking at 250 F. to 400 F. and the resulting `dimers can be recovered in high yields under controlled temperatures.

To accomplish the selective dimerization of the acyclic dienes favorably, cyclic dienes which would interfere are removed by prior treatments of selective dimerization and fractionation under conditions which leave the acyclic dienes substantially unaffected. The favorably formed dimers 4of the acyclic dienes are free of less stable codimers. They can be formed with a minimum of high molecular weight polymers.

Cycloalkadienes, isoprene, piperylene, hexadiene, and other C5 through Cs diolens or dienes are formed in vapor phase cracking of naphtha through gas oil petroleum hydrocarbons at elevated temperatures, e. g. 1000 F.-l400 F. These dienes are mixed in complex streams with mono-oleins, aromatics, and relatively small amounts of parafns and naphthenes.

The present invention is not concerned with the particular cracking operations or method of fractionation of the cracked products up to the point Where streams are obtained which include the C5 and higher hydrocarbons. One method of cracking to obtain the high yields of diolens employs large amounts of steam and relatively low pressures, such as directed in U. S. Patents 2,363,903 and 2,348,659. Catalytic dehydrogenation and cracking processes may be used to supply the diene-rich streams.

A discovered basis for the present invention resides in the determination of how the acyclic dioleiins are selectively dimerized and how they can be separated mainly as dimers or low molecular weight polymers from the described complex streams of olenic and aromatic hydrocarbons. The thus recovered low molecular weight polymers or dimers of the noncyclic dioleiins are useful as substitutes for materials like dipentene, and other terpene derivatives, or they may be subjected to cracking to recover the monomers, such as isoprene, piperylene, hexadienes, etc. in concentrated form.

The preferred method of recovering the dimers selectively comprises two separate thermal dimerizing stages. In the rst dimerizing stage, cyclic diolens are selectively dimerized under proper conditions to prevent dimerization and codimerization of the acyclic dioletns. This rst dimerizing is ,followed by fractional distillation to distill the undimerized hydrocarbons from the dimer product under conditions which prevent dimerization of the acyclic ldioleiins and prevent decomposition Vof the Vcyclic dioletin dimers. In the second dimerization stage, all or any fraction of the distilled acyclic diolefin mixture can be subjected to thermal dimerization at selected elevated temperatures. The dimer product of this second dimerization can be distilled to recover dimers and low monomeric decomposition products.

. In an additional embodiment of the invention, the dimers, codimers, and higher polymers formed from the acyclic diolefns are treated at elevated temperatures to obtain their decomposition and reformation of monomers.

In the drawing are shown simplified flow plans of operations involved by the invention.

Section A pertains to operations wherein cyclic dienes are dimerized and separated.

Section B pertains to operations of separating the acyclic dienes for separate 2nd stage dimerization.

Section C pertains to operations of depolymerizing or cracking the polymers of acyclic dienes.

In operations of section A illustrated, a suitable Cs-iunsaturated and aromatic hydrocarbon fraction, essentially containing cyclopentadiene, isoprene, and piperylenes, is charged by line 1 as feed stock to the dimerizer 2. By holding the charging stock in the dimerizer vessel 2 at temperatures within the range of 180 to 240 F. for about 4 to 12 hours, preferably at 200-220 F. for about 6 to 8 hours, substantially all the cyclopentadiene becomes dimerized selectively. This selective dimerization of the cyclic diolens can be carried out under such controlled temperatures and controlled periods to obtain practically or nearly complete dimerization of the cyclic diolefins with negligible eifect on the acyclic diolens.

The dimerization product from dimerizing vessel 2 is discharged through line 3 into an intermediate part of fractionator 4 Where the unreacted acyclic dienes are to be separated from the dimers left as a bottoms product.

In fractionator 4, having about 30 plates, the temperatures are maintained from top to bottom for rapid distillation of Cs-Cg hydrocarbons overhead in order to leave the Cnr-{- dimer concentrate as bottoms with a minimum polymerization of acyclic diolens being distilled. A limited amount of decomposition of the cyclic diolen dimer is allowed to occur. This dimer residual product is Withdrawn continuously and promptly `as the desired cycloalkadiene dimer product by -line S.

Fractionating column 4 may be operated under vacuum but preferably is operated under pressures slightly above atmospheric pressures, from about 0 to 15 pounds per square inch gauge with some steam introduced by line 6 near the bottom of column 4. Added heat is supplied to the bottom of column 4 by the injected live steam and with the aid of additional heat exchange means, if necessary, to maintain the bottoms liquid at temperatures between 280 and 300 F. Sutlicient cool reux is supplied at the top of fractionator 4 to maintain a temperature of the overhead vapors `in a range of -180 F., preferably in the range of to 170 F.

The vapors are withdrawn overhead from column 4 through line 7 to a partial condenser v8 which supplies the reux returned through line 9 to the top of column 4.

The remaining overhead vapors from column 4 are passed by line 10 to the second stage dimerizer unit 11 unless they are first subjected to a fractionation, which makes a separation between the noncyclic dioleiins as will be explained in connection with section B.

In the second stage dimerizer 11, the temperatures and residence period are essentially higher than in the first stage to accomplish selective thermal dimerization and codimerization of the non-cyclic dioleiins, especially the Cs-,Cs dioleiins, such as isoprene, piperylene, or hex-adienes, depending upon which of these are present in the feed to the second stage dimerizer 11.

In the second stage dimerizer 11, a thermal soaking temperature in the range of 250 to 400 F. for about 12 to 24 hours brings about practically complete dimerization and polymerization of the Cs-Ca diolens, even if all the diolens are acyclic. The time required is shortened if the temperature is increased, but with increase in temperature there is a tendency to overpolymerize, i. e., form complex polymers or" of higher molecular weight than the trimer. Preferred conditions for this second stage dimerization are 300 to 400 F. for 12 to 20 hours and pressures of about 40 to 400 p. s. i. g.

'To separate and recover .the acyclic diene dimers, eflluent from the second stage dimer v11 is passed by line 12 into fractionator 13. Fractionator 13 may have about 25 to 30 plates and receive the feed from line `12 at about the 10th to 15th plate. The hydrocarbons lower boiling than the dimer are taken overhead fromV fractionator 13 at vapor temperatures of about 160 to 170 F. through line 14 to partial condenser 1S. Reflux is returned by line 16 to the upper part of column 13. The remaining overhead vCs to Ca vapor stream substantially free of diolens is withdrawn through line 17. This vapor stream substantially free of diolefins is in suitable condition for recovery of aromatic hydrocarbons s uch as benzene and toluene, e. g. by extractive distillation with any of the well-known solvents, including phenols, furfural, diethylene glycol, etc.

The ,dimer and higher polymer bottoms should be heated at the bottom of fractionator 13 to a temperature of about 300-340 F. to be stripped well of lower-boiling hydrocarbons. These bottoms can then be transferred by line 18 into a second fractionator 19 to segregate the dimers.

In fractionator 19 the dimers may be distilled as overhead vapors. These dimer vapors are removed by line 20 at temperatures in the range of 300 F.400 F. to the partial condenser 21. The partial condensate boiling in the range of 360 F.400 F. is returned to the upper part of column 19 by line 22, the remaining vapor stream of dimers is withdrawn by line 23 to a complete condenser or recovery system, not shown.

An intermediate fraction boiling in the range of 400 F.-500. F. may be withdrawn from column 19 as a side stream by line 24. This side stream may be removed about l to l2 plates below the feed plate. The bottoms comprising high boiling polymers or resins are withdrawn at vtemperatures of about 500 to 560 F. by line Z5.

In the modified operation shown in section B, the same operational steps and conditions as described with respect to section A up to the second stage dimerizer are used; but between fractionator 4 and the second stage dimerizer 11, the overhead stream from column 4 is lirst fractionated in column 30. The Cs-Cs stream freed of cyclodienes is sent by line 31 from line 10 into an intermediate part of column 30. Column 30 is operated to distill overhead the hydrocarbons boiling up to and very close to 100 F. The vapors taken overhead from column 30 by line 32 include most of the isoprene, some pentanes, pentenes up through trimethyl ethylene, but should be kept relatively free of piperylenes, cyclopentene, and Cs-l hydrocarbons. An intermediate fraction boiling in the range of 100 to 115 F. contains the piperylene and is withdrawn as a side stream by line 33. Higher-boiling hydrocarbons are withdrawn from the bottom of tower 30 through line 34.

Any of the fractions desired may be sent from fractionating column 30 to the 2nd stage dimerizer 11 through feed line 35 by lines 36, 37, and 38.

Etiiuent from the second stage dimerizer 11 is fractionally distilled in fractionating tower 13 in the manner described to distill over (Q-Cs components. The Cia-Cs fraction free of diolens is withdrawn overhead from column 13 by line 14 to partial condenser 15 which provides reux returned by line 16 and leaves the lrarueiuiugdiolen free stream `to be withdrawn by line 17. Live steam injected near the bottom of column 13 helps prevent thermal decomposition of the dimers, codimers, and higher polymers being separated as a residual product. This residual product should not .be heated t0 a temperature much above 39.0 F- for any substantial peried 0f time .it .it desired t0 eweid coutamiueting the gverheed et 13 by dielen meno.-

4 mers or loss thereof which would result from decomposition of dimers and higher polymers.

The dimers and polymers withdrawn as bottoms from column 13 through line 40 or from column 19 by lines 25 and 26 may include components relatively unstable at temperatures of about 300 to 340 F. These bottoms materials may be passed by line 41 to a suitable heating vessel 42 .for heating to .temperatures ,suiciently high to accomplish 'a certain amount of thermal decomposition within a reasonable period, for example, to temperatures of 400 F. to l000 F. A heating tube furnace or a heated series Aof vessels, not shown, may be used for heating the polymers.

Efliuent decomposition Aproducts and undecomposed polymers are passed from vessel 42 through line 43 into fractionator 44. Fractionator 44 is operated as a rerun column under conditions similar to those described with respect to column 13. Vapors are taken overhead from column 44 by line 45 at temperatures of about 160 to F. Partial condensate collected in the condenser 46 is returned as reflux by line 47 and the remaining steam containing monomeric diolens is withdrawn by line 48. Live steam may be injected to aid in maintaining a suitable temperature of about 300 F.340 F. in the bottoms liquid of column 44. The bottoms dimer and higher polymer product from fractionator 44 is delivered by line 50 into fractionator 51, which is operated in a manner similar to column 19. Dimers of Cs-Cs noncyclic diolens are taken overhead through line S2 from column 51 to partial condenser 53 which supplies liquid reflux for line 54 and a remaining vapor product withdrawn through line S5. Trimer product may be withdrawn as a side stream through line 56. Bottoms polymer product boiling above 500 F. is withdrawn from column 51 through line 57. Steam at about 500 to 600 F. is supplied to column 51.

Each o f .the fractionators 13, 19, 44, and 51 are equipped for introduction of live steam by lines 59, 60, 61, and 6 2, respectively.

Experimental and analytical determinations demonstrating how the invention can be used to recover the vseveral different products are shown in the following examples:

EXAMPLE 1 A number of vapor phase cracked Cs-Cs hydrocarbon fractions were subjected to thermal soaking in liquid phase at temperatures in the range of 180 F. to 240 F. for periods ranging from 24 hours to about 6% hours. Pressures of 50 to 400 p. s. i. were applied during the soaking treatments.

A thermal soaking of the streams containing both cyclic and noncyclic dioleins at about 200 F.-220 F. for 6 to 8 hours gave approximately 90% selective dimerization of the cyclic dioleiins.

Beginning at 240 F., as the dimer yield was increased, it was accompanied by an appreciable reduction in purity indicating codimerization of the cyclic with acyclic diolefins.

It was demonstrated and confirmed that the cyclic diolelins can be selectively dimerized to the exclusion of dimerization or codimerization by acyclic dioleiins present therewith. Bottoms dimer concentrates withdrawn from column 4 by line 5 were analyzed to have cycloalkadiene purities above 85%.

EXAMPLE 2 An overhead vapor stream separated from dimerized cyclodienes as described with reference to fractionating column 4 was subjected to thermal soaking at 300 F. for 1 6 hours. The thus thermally soaked product was fractionally distilled under vacuum and the bottoms dimer to heavy polymer fraction was analyzed.

The yield of 13-15 weight percent dimerized material boiling above 338 F. obtained indicated good recovery -include dimers and codimers of isoprene, piperylene, and

hexadienes.

EXAMPLE 3 A'second stage thermal'soaking was applied as in vessel 11, to overhead materials of Cs-Cs fraction containing cyclopentadiene and methyl cyclopentadiene. The second stage dimerization was carried out at 300-310 F. for approximately 18 hours. The second stage soaked material was reduced by distillation under a vacuum 50 mm. Hg pressure with removal of overhead vapors at 80 C. (176 F.). The dimerized material was passed through a tube and cracked at a temperature of 700 F.

. to '900 F.

The cracked product was fractionated to remove vapors boiling up to 167 F. The low-boiling fractions boiling below 167 F. were analyzed and found to contain acyclic dioletn monomers in substantial quantities.

In carrying out soaking of a fraction containing the cycloalkadienes with acyclic dienes at temperatures beginning at about 240 F., dimerization and codimerization of the acyclic dienes took place to a substantial eX- tent.

In conjunction with this experiment it was demonstrated that a second stage dimerization at 250 F. to about 300 F. or to about 320 F. can be used advantageously to remove any cyclic dienes remaining in the overhead stream from fractionator 4.

Table I [Dmers from 300 F. thermal soakingj.

. Ultra Violet Yield, Analysis ol Monomer Wt. Fraction 1 (Percent) Cyclopen- Mcthylcyclotadiene pentadiene Tubo Cracking (700 F.):

I P- F 20.2 11.6 20.7 Tube Cracking (900 F.):

IBF-167 F 13. 3 8. 8 34.0

l Tube cracking temperature was raised to 900 F. after all material up to 167 F. vapor temperature was removed at 700 F. temperature.

The data indicated that, in addition to the amounts of cyclic diolens, other diolen monomers were formed by the cracking. The higher cracking temperatures tend to crack out relatively more methyl cyclopentadiene, evidently existing in relatively more stable codimers with the acyclic Cs-Ca diolens.

EXAMPLE 4 A C5 diolen stream having negligibly small amounts (0.5 wt. percent) of cyclopentadiene and methyl cyclopentadiene present was subjected to thermal soaking at temperatures in the range of 300 to 400 F. The isoprene dimer and codimer product formed was analyzed.

' Nearly 95 volume percent of the product distilled in the range of 324 to 342 F.

EXAMPLE 5 hours. It was possible to obtain a product boiling entirely above 300 F., thus indicating good conversion to dimers and polymers. About 75% of the thermally soaked product boiled in the dimer range of 300 to 344 F. in soaking the piperylene free of the cycloalkadiene.

EXAMPLE 6 A representative C5 fraction rich in dienes to be processed contained 15-20 weight percent isoprene, 10-15 weight percent cyclopentadiene, 10-15 weight percent piperylene, 5 weight percent other dienes, 15-20 weight percent tertiary olefins, 20-25 weight percent normal olens, and 2-5 weight percent parains.

It is well known that the separation between such dioletins has required in the past expensive superfractionation combined with extractive distillation steps.

With the object of recovering high purity isoprene and a separate piperylene dimer product more eiliciently, the C5 fraction is subjected to thermal soaking as ing-the first stage dimerizer 2 at 180240 F. to dimerizecyclopentadiene without reacting the isoprene or piperylenes in about 6 to 12 hours. The thermally soaked liquid material fed into a fractionator, like column 4, having 20 plates can be distilled and fractionated in such a column to obtain an overhead stream having an end point of about F., the bottoms temperature of column 4 being maintained at below 300 F. with a pressure up to 15 p. s. i. g. in the column.

The overhead stream from column 4 can be made substantially free of cyclopentadiene by keeping the bottoms temperature suiciently'below 300 F. following adequate thermal soaking. However, if the overhead from column 4 contains an appreciable amount of cyclopentadiene, or methyl cyclopentadiene, this overhead fraction can be subjected to a second thermal soaking at moderately elevated temperatures of 250 to 300 F. to effect further dimerization of the cyclic diolefms and, to a slight extent, some codimerization thereof with a small amount of isoprene and piperylene.

Passing the undimerized C5 fraction containing isoprene and piperylene but substantially free of cyclopentadiene into a fractionating column represented, for eX- aniple, by column 26 in the drawing, this column can be operated to have a temperature of about 100 F. in the overhead vapors and a temperature of about F. in the bottoms under a pressure of 15-20 p. s. i. g. With about 50 plates in this column and the feed stream entering near the 25th plate, an isoprene fraction boiling up to 100 F. can be taken overhead in excellent condition for extractive distillation without the interference by the other diolens. A bottoms fraction containing the piperylene can then be thermally soaked, as in the second stage dimerizer 11, :at 250400 F. until practically all the piperylenes are dimerized. The piperylene dimer then is recovered as an intermediate fractional distillate.

The piperylene dimer product produced as described has been indicated to be useful for many purposes. One particular use of the piperylene dimer is that of a feed stock for sulfurization in forming sulfurized lubricating oil additives. The high quality dimer product obtained has an ASTM boiling mainly in the range of 322 F. to 344 F.

EXAMPLE 7 A Cs-Cs overhead fraction containing isoprene and piperylenes distilled away from a cyclopentadiene dimer concentrate was thermally soaked at 300 F. for 24 hours, ythen fractionated to recover the dimer, trimer, and higher polymer products.

The total dimer, trimer and polymer product formed, stripped of unreacted C5 to C6 hydrocarbons, had an A. P. l. gravity of 27.1 at 60 F. This total product was subjected to vacuum distillation and analyzed into the following cuts:

Vol. Gravity, Percent Boiling Range J4.6012. I. a

60 295 to 400 F 31. 3 20 425 t0 518 F 24. 6 20 Bottoms 20. 6

The iBP400 F. crude dimer out I was water white in color. The 400-500 F. crude trimer cut II was light yellow. The bottoms fraction was yellow orange.

EXAMPLE `8 Part of the dimerization vproduct was cracked to recover monomers, and the residual uncracked polymer product was analyzed as having the following characteristics:

Boiling range- 90 vol. percent 194 to 435 F. 10 vol. percent 302 to 365 F. l vol. percent 365 to 435 F.

iodine No 257.

Sp. gravity 0.9458.

These polymers were thus found to be of proper characteristics for use as rubber reclaiming oils needed'for softening and swelling natural or .synthetic rubber.

It is to be understood that the vinvention is not to be limited by the specific examples and that other modifications come within its scope.

Having described the invention, it .isi claimed as follows:

1. A process for separating and recovering cyclic Cs-Cs diolens as dimers and polymers and .separately Cs-Cs acylic diolens as dimers and higher polymers from a cracked hydrocarbon fraction rich in monomers of the Ca-Ce diolens, which comprises thermally .soaking said fraction at temperatures in the .range of 180 to 240 F. for about 4 to l2 hours until the cyclic dioletins present in said fraction are dimerized -selectively with negligible dimerization and negligible codimerization of the acyclic diolefins, fractionally distilling the undimerized components of said .fraction including said acyclic diolens from the resulting cyclic diolen dimer and polymer product, passing the distilled undimerized components containing the acyclic diolens into ,a second thermal soaking zone, subjecting the acyclic diolens to thermal soaking for about .12 to 24 hours at temperatures in the range of 250 .to 400 F. in said second `thermal soaking zone, then fractionally distilling the resulting product from the second thermal soaking vzone to remove unreacted acyclic diolen monomers from a bottoms liquid heated to 300 to 340 F., and fractionating said bottoms 8 liquid to separate an intermediate fraction of acyclic diolefn dimers boiling in the range of 300 F. to 400 F. from higher boiling trimers and polymers.

2. A process as described in claim 1, wherein said undimerized components fractionally distilled from the dimerized and polymerized -cyclic diolens boil in the range of to 115 F. and are rich in piperylene but substantially free of cyclodienes.

3. In a process of separating and recovering isoprene and piperylene as dimers from a diene-rich Cs-Cs fraction containing a relatively small amount of cyclopentadiene and methyl cyclopentadiene, the steps which comprise heating said fraction Vto temperatures of 250 F. to 300 F. for about l2 to 20 hours to dimerize and polymerize said cyclopentadiene, then fractionally distilling the remaining unreacted isoprene and piperylene monomers from dimers and polymers of the cyclodienes, passing the resulting fractionally distilled acyclic diene monomers substantially free of cyclodienes into a second soaking zone, dimerizing and polymerizing the acyclic dienes thus freed of said cyclopentadienes in the second soaking zone at a temperature .in the range of 250 to 400 F. for about 12 to 24 hours to obtain an acyclic diene dimer and higher polymer products, heating said dimers and higher polymer products to a temperature of 300 to 340 F. in stripping lower boiling hydrocarbons therefrom, thereafter separating the acyclic dimer product boiling mainly in the range of 322 F. to 340 F. from higher polymers of the acyclic dienes.

4. In a process of recovering dimers from higher polymers of a C5 acyclic diene free of cyclopentadiene, the steps whichcomprise dimerizing and polymerizing the C5 acyclic diene at a temperature in the range of 250 to 400 F. in a period of 12 to 24 hours, fractionally distilling from the resulting dimers and polymers unreacted acyclic dienes and polymers heated to a temperature in the range of 300 to V340 F., and thereafter fractionally distilling said dimers in a separate fractionation zone from the higher polymers of the acyclic diene heated to a temperature in the range of 400 to 560 F.

5. In a process of recovering dimers of acyclic C5 dienes free of cyclopentadiene dimers, the steps which comprise dimerizing and polymerizing said acyclic dienes free of cyclopentadiene at 250 to 400 F. in 12 to 24 hours, stripping resulting dimer and higher polymer products of hydrocarbon components boiling below 300 F., fractionally distilling the acyclic diene dimer from the higher polymer products, and heating said higher polymer products to a temperature in the range of 400 to 1000 F. to decompose the higher polymers linto lower boiling products including monomers and dimers and vfractionating the resulting decomposition products including monomers and dimers from said higher polymer products which were heated to decomposition to obtain additional separated dimer of the acyclic diene.

References Cited in the le of this patent UNITED STATES `PATENTS 2,211,038 Ward Aug. 13, 1940 2,397,580 Ward Apr. 2, 1946 2,401,414 Domani et al. June 4, 1946 2,508,922 Luten et al. May 23, 1950 

1. A PROCESS FOR SEPARATING AND RECOVERING CYCLIC C5-C6 DIOLEFINS AS DIMERS AND POLYMERS AND SEPARATELY C5-C6 ACYLIC DIOLEFINS AS DIMERS AND HIGHER POLYMERS FROM A CRACKED HYDROCARBON FRACTION RICH IN MONOMERS OF THE C5-C6 DIOLEFINS, WHICH COMPRISES THERMALLY SOAKING SAID FRACTION AT TEMPERATURES IN THE RANGE OF 180* TO 240* F. FOR ABOUT 4 TO 12 HOURS UNTIL THE CYCLIC DIOLEFINS PRESENT IN SAID FRACTION ARE DIMERIZED SELECTIVELY WITH NEGLIGIBLE DIMERIZATION AND NEGLIGIBLE CODIMERIZATION OF THE ACYCLIC DIOLEFINS, FRACTIONALLY DISTILLING THE UNDIMERIZED COMPONENTS OF SAID FRACTION INCLUDING SAID ACYCLIC DIOLEFINS FROM THE RESULTING CYCLIC DIOLEFIN DIMER AND POLYMER PRODUCT, PASSING THE DISTILLED UNDIMERIZED COMPONENTS CONTAINING THE ACYCLIC DIOLEFINS INTO A SECOND THERMAL SOAKING ZONE, SUBJECTING THE ACYCLIC DIOLEFINS TO THERMAL 